provide a simple light theme

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: print usage string

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
rounded corners in the menu

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
gui: add menu

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>